Our section has a major effort on understanding the molecular and cellular basis of stuttering, a common but poorly understood speech disorder. Stuttering has long been known to have a genetic component. We have recently identified mutations in the GNPTAB, GNPTG and NAGPA genes that are associated with stuttering in populations worldwide. These results indicate that stuttering can be associated deficits in the lysosomal targeting pathway. A goal of our current research is to identify how the subtle metabolic defects caused by mutations in these three genes lead to stuttering without any other discernible symptoms. These studies are focused on using neuroimaging and neuropathology methods the identify brain tissue pathologies in individuals carrying different mutations in these genes. We are also working to develop a mouse model of human stuttering. This is being done by creating so-called knock-in strains of mice that carry the mutations identified in humans who stutter. These experiments require a detailed acoustical analysis of mouse vocalization, which is largely ultrasonic in nature. In these experiments, we are working with Drs. Terra Barnes and Tim Holy at Washington University in St. Louis, who are leaders in the study of mouse vocalization. Preliminary results indicate that the presence of human stuttering mutations causes reproducible alterations in mouse vocalizations, and that these alterations show parallels with the alterations present in the speech of individuals who stutter. We are also collaborating with Dr. Peter Vogel at St. Jude's Hospital in Memphis, TN to examine any microscopically observable neuropathology that may accompany the vocalization deficits we observe in mice carrying human stuttering mutations. In a parallel line of inquiry, we are working with Dr. Stuart Kornfeld, also at Washington University in St. Louis. Dr. Kornfeld is a world leader in the study of the enzymes encoded by the GNPTAB, GNPTG, and NAGPA genes. The goal of these studies is to better understand the effects of the mutations observed in human stutterers on the function of these enzymes at the molecular and cellular level. Initial results in our analysis of mutations of the NAGPA gene found in stuttering indicate that these mutations reduce the activity of this enzyme by about half, and cause it to be mis-localized and/or more rapidly degraded than the normal version of this enzyme. In the past year we have continued our studies in a group of families from Cameroon, West Africa, which each have many cases of persistent stuttering. Our studies of the largest of these families have shown that there is more than one causative gene (at more than one location) at work in this large family, and we have identified significant linkage on chromosomes 2, 3, 14, and 15. At the locus on chromosome 15, we have identified mutations in the AP4E1 gene that are associated with stuttering in populations worldwide. We are currently collaborating with Juan Bonificino, PhD, of the NICHD, who is the discoverer of the AP4 complex, to understand the functional effect of the mutations in this gene observed in stuttering. Additional studies in stuttering families from Brazil have identified a new stuttering gene localization on chromosome 10. Our studies of taste perception are focused on the role of genetic differences in taste perception in tobacco use, particularly the use of mentholated cigarettes, which are disproportionately used by African Americans. Our goal is to determine whether this disproportionate use is associated with genetic differences, specific to African Americans, in genes that encode taste perception machinery. This study is being done in collaboration with the University of Texas Southwestern Medical Center, using the well-characterized Dallas Heart Study population. In the past year, we have also entered into a collaboration with Dr. Thomas Kirchner of the Legacy Foundation for Tobacco Research and Dr. Carla Berg of Emory University, who together have provided >1700 DNA samples from individuals with known smoking phenotypes. Sequencing of the TRPM8 gene, encoding the menthol receptor, is underway in our lab.